Centering target



v Feb. 28, -192s.

H. CRONJAEGER CENTERING TARGET Filed. Nov. 15. 1926' 1IIIIIIIIIIIIA TESS Par

HANS oRoNJAEGEn, "on nALtn-oN-THE-sAAtE, GERMANY.

cnn'rERInG TARGET.

Application filed November 15, 1926, Serial No. 148,589, anaiajeermany April 27, 1925.

My invention relates to theodolites, transits, levels and'other'like instruments, usedin surveying above and under ground, and more especially to theart of facilitating the. proper location of such an instrument so'as to cause its vertical main axis to accurately aline and register with the marked point above which or under which the instrument is set for use. n J

It has been common practice in surveying to use for the purpose under consideration a plumb-bob, suspended by acord from the stem of the instrument and to shiftthe latter on' the tripod plate until it registers with the marked point. This method how ever is subject to serious inaccuracies for the reason that in surveying above ground the wind and in surveying under ground the air-current forced through the mine for ventilating the latter will obviously cause the plumb-bob to freely swing to and frowhich renders the correct locating of the in-' strument a diflicult and tiresome task.

Various other methods have been proposed for optically locating surveyors instruments centrally over markedpoints: As far back .as 1888 a German inventor suggested in his German Patent 47061 to provide a vertical borehole in the stem of the theodolite,and to aim in the direction of the point of reference tlIIOU lI the vertically tilted and fixed telescope of the instrument. l

Other inventors have provided auxiliary devices as telescopes, reflecting mirrors, (see e. g. U. S. Patent 835,711), attachable to, the main'instrument for optically centering the latter. These optical methods however 1 have also serious disadvantages: Experience shows, that'the original, proper adjustment of the auxiliary device relative to the main instrument will soon be lost through various causes as changes of temperature, humidity, dust, knocking-about, etc., that the, whole instrument must constantly be kept under control, and that the inaccuracies in taking measurements introduced by improperly adjusted auxiliary centering devices of the types mentioned are much greater" than thoseentailed by thesimple method'of plumbing.

Another drawback experienced in the above outlined optical method consists therein that it is extremely difii cillfiland' tiresome for the operator to locgTthFmarked point at all through thertelescope 'byireasm of its limited space. of vision atshort distances which mostly" is not greater than the diameter of the lenses of the instrument, and

also by reason of the specific nature of the marked l'point, viz its invisibilityf In surveying, many points-of reference are found pipe driven into the ground orby across roughly carved into a stone or the like.

Marks of thls character as tubes, stones and the like generally have no visible real of center-point and are often hard to locate even wlth the naked eye by reason of their indifi'erent color and shape not strongly disto be markedsimply by a short piece of steel 7 the misplacing of the surveying instrument in making measurements by reason of the comparatively short sights to be taken has much more serious consequences.

The object of my invention is to, overcome the said drawbacks and difiiculties in surveying above and underground'and to dispense altogether with a plumb and with auxiliary optical devices attached. to and used in connection with the main instrument.

,Another object of my invention is to rovide novel means for temporarily mar ring points of reference in surveying in a special and advantageous manner so as to renderit easy to locate the latter with the main teleon scope of the instrument.

Anotherobject of my invention is to design an auxiliary marking device for the purpose under consideration which enables the operator to easily and speedily mark the ,;rea:l :centrum of the tube, stone, etc. serving as a mark of reference.

The nature and scope of my' inventionis outlined in the appended claims and will be .F/i g. .1 is a diagrammatic, partly perspectiveiv-iew, showing the application, of my fixedpoint,

Fig. 2 is a similar view showing the application of this invention in centging ia' j mor'effully understood from the following specification taken together with the accompanyingf'drawing, wherein invention in centering a ,theodolite abovea 106 example a marking platetobe used in ac: cordance with this invention.

Figs. 5 and 6 show a structurally modified I .tate the accurate placing of the marking marhng plate in cross section and plan, respectively. v

While I have shown my method and a device for carrying out the same into practlce as a plied-to theodolites-and will describe it for convenience, its use is not restricted to surveying instruments, as it may be appliedto other instruments having a tiltable telescope which must be set up for use over or below a given point.

Referring to Fig.

the centering of the theodolite, I propose to provide the stem at and the other supporting and clamping members of the instrument 1n-' cluding the tripod-plate with a central view hole 0, 0 extending vertically and axially through said supporting members, so as to enable the operator to aim through the vermay be a tube,

tically tilted telescope at the object (Z which stone, wooden pole, or any other object used for marking fixed points andto shift the instrument to and fro on the tripod-plate until its axisis in alinement with the 'point of reference.

I am aware that exactly the identical suggestion has been made before in the above mentioned German Patent 47061 of 1888.

. In said case however an additional centering device is required for approximately adjusting the instrument above the fixedpoint, 'viz', a plumb which is to be hung from'a hook, temporarily screwed into the view hole. The necessityof a lumb device with p its'drawbacks set forth a ove for primarily centering the instrument fully illustrates the difficulties experienced in locating the fixed point with the telescope alone.

In order to dispense with a plumb altogether and with other centering devices at-- tached to the telescope as referred to above, and to enable the operator to easily and speedily locate the fixed point with the telescope alone, I propose to place a s 'ecially designed marking plates centrally a ove or below the object containing 'thefixed point of reference.

.As seen in Figs. 3-5, the markin plate according to this invention is of pre erably circular shape and is provided with radial lines f, f", f radiating from its center and with a number of concentric lines 9', g, g Y Y Each of the radial lines f serves as a guide line (directrix) to the operator after he has located the marking plate, enabling him to shift at once the instrument in the direction to the center of the marking plate, which 00-- it will be understood that 1 in order to. fac1litate other transparent circular inoides polnt.

. facilipla-tee centrally on objects having a circular cross section as in the case of a pipe, the

upperopen end serving as a substitute for Both tlie radial -aind the concentric guide lines will jointly facilitate the accurate placing of the marking plate on a stone or the like having a cross carved at its top, 1nd1- eating the point of reference.

Marking plates according to this invention are made of glass, mica,

"or translucent material and may be in the form of a disc of uniform thickness or may be formed like a lens with convex or. c'oncavesurfaces as indicated in Fig. 5. I prefer to mount themarking plate 6 in a rim k, so as to increase its weight, to prevent its being blown off by the wind and to .make it more convenient for handling, more rigidand less subject to be damaged.

' The guide lines 7 and 9 should be made in celluloid or 1 different colors, e. g. white, light-green, and

yellow alternating. In'cases where the in mines and other dark places under groun the guide lines 7, g and the rim It should be coated with a fluorescent substance. I

According to' this invention the marking plate 6 is provided-with a small hole 11 in its center so that it can be fixed in its position by a nail or be hung up underneath the fixed oint ii -mines, as indicated in Fig. 2., In the latter case an objective lc having a prism or a mirrorshould be temporarily attached to the ordinary objectiveof the telescope.

2. A target .as inclaim- 1, characterized 'marking plate is predominantly to be used 7 for centering theodo- I therein, that the marking platei is of lens shape in cross sect-ion and a rim-in which said target is mounted.

In testimony whereof I have signed my name to thisspecification.

' HANS GRONJAEGER. 

